The present invention relates to surgical ablation instruments for ablation of tissue for the treatment of diseases, and, in particular, to surgical instruments employing radiant energy. Methods of ablating tissue using radiant energy are also disclosed. The instruments can be used, for example, in the treatment of cardiac conditions such as cardiac arrhythmias.
Cardiac arrhythmias, e.g., fibrillation, are irregularities in the normal beating pattern of the heart and can originate in either the atria or the ventricles. For example, atrial fibrillation is a form of arrhythmia characterized by rapid randomized contractions of the atrial myocardium, causing an irregular, often rapid ventricular rate. The regular pumping function of the atria is replaced by a disorganized, ineffective quivering as a result of chaotic conduction of electrical signals through the upper chambers of the heart. Atrial fibrillation is often associated with other forms of cardiovascular disease, including congestive heart failure, rheumatic heart disease, coronary artery disease, left ventricular hypertrophy, cardiomyopathy or hypertension.
Various surgical techniques have been proposed for the treatment of arrhythmia. Although these procedures were originally performed with a scalpel, these techniques may also use ablation (also referred to as coagulation) wherein the tissue is treated, generally with heat or cold, to cause tissue necrosis (i.e., cell destruction). The destroyed muscle cells are replaced with scar tissue which cannot conduct normal electrical activity within the heart.
For example, the pulmonary vein has been identified as one of the origins of errant electrical signals responsible for triggering atrial fibrillation. In one known approach, circumferential ablation of tissue within the pulmonary veins or at the ostia of such veins has been practiced to treat atrial fibrillation. Similarly, ablation of the region surrounding the pulmonary veins as a group has also been proposed. By ablating the heart tissue (typically in the form linear or curved lesions) at selected locations, electrical conductivity from one segment to another can be blocked and the resulting segments become too small to sustain the fibrillatory process on their own. Ablation procedures are often performed during coronary artery bypass and mitral valve replacement operations because of a heightened risk of arrhythmias in such patients and the opportunity that such surgery presents for direct access to the heart.
Several types of ablation devices have recently been proposed for creating lesions to treat cardiac arrhythmias, including devices which employ electrical current (e.g., radio-frequency xe2x80x9cRFxe2x80x9d) heating or cryogenic cooling. Such ablation devices have been proposed to create elongated lesions that extend through a sufficient thickness of the myocardium to block electrical conduction.
These devices, however, are not without their drawbacks. When cardiac surgery is performed xe2x80x9con pump,xe2x80x9d the amount of time necessary to form a lesion becomes a critical factor. Because these devices rely upon resistive and conductive heating (or cooling), they must be placed in direct contact with the heart and such contact must be maintained for a considerable period of time to form a lesion that extends through the entire thickness of the heart muscle. The total length of time to form the necessary lesions can be excessive. This is particularly problematic for procedures that are performed upon a xe2x80x9cbeating heartxe2x80x9d patient. In such cases the heart, itself, continues to beat and, hence, is filled with blood, thus providing a heat sink (or reservoir) that works against conductive and/or resistive ablation devices. As xe2x80x9cbeating heartxe2x80x9d procedures become more commonplace (in order to avoid the problems associated with arresting a patient""s heart and placing the patient on a pump), the need for better ablation devices will continue to grow.
Moreover, devices that rely upon resistive or conductive heat transfer can be prone to serious post-operative complications. In order to quickly perform an ablation with such xe2x80x9ccontactxe2x80x9d devices, a significant amount of energy must be applied directly to the target tissue site. In order to achieve transmural penetration, the surface that is contacted will experience a greater degree of heating (or freezing). For example, in RF heating of the heart wall, a transmural lesion requires that the tissue temperature be raised to about 50xc2x0 C. throughout the thickness of the wall. To achieve this, the contact surface will typically be raised to at least 80xc2x0 C. Charring of the surface of the heart tissue can lead to the creation of blood clots on the surface which can lead to post-operative complications, including stroke. Even if structural damage is avoided, the extent of the lesion (i.e., the width of the ablated zone) on the surface that has been contacted will typically be greater than necessary.
Ablation devices that do not require direct contact have also been proposed, including acoustic and radiant energy. Acoustic energy (e.g., ultrasound) is poorly transmitted into tissue (unless a coupling fluid is interposed). Laser energy has also been proposed but only in the context of devices that focus light into spots or other patterns. When the light energy is delivered in the form of a focused spot, the process is inherently time consuming because of the need to expose numerous spots to form a continuous linear or curved lesion.
In addition, existing instruments for cardiac ablation also suffer from a variety of design limitations. The shape of the heart muscle adds to the difficulty in accessing cardiac structures, such as the pulmonary veins on the anterior surface of the heart.
Accordingly, there exists a need for better surgical ablation instruments that can form lesions with minimal overheating and/or damage to collateral tissue. Moreover, instruments that are capable of creating lesions uniformly, rapidly and efficiently would satisfy a significant need in the art.
Surgical ablation instruments are disclosed for creating lesions in tissue, especially cardiac tissue for treatment of arrhythmias and the like. The hand held instruments are especially useful in open chest or port access cardiac surgery for rapid and efficient creation of curvilinear lesions to serve as conduction blocks. The instruments can be applied to form either endocardial or epicardial ablations, and are designed to create lesions in the atrial tissue in order to electrically decouple tissue segments on opposite sides of the lesion.
In one aspect of the invention, hand-held and percutaneous instruments are disclosed that can achieve rapid and effective photoablation through the use of penetrating radiation, especially distributed radiant energy. It has been discovered that radiant energy, e.g., diffuse infrared radiation, can create lesions in less time and with less risk of the adverse types of tissue destruction commonly associated with prior art approaches. Unlike instruments that rely on thermal conduction or resistive heating, controlled penetrating radiant energy can be used to simultaneously deposit energy throughout the full thickness of a target tissue, such as a heart wall, even when the heart is filled with blood. Distributed radiant energy can also produce better defined and more uniform lesions.
It has also been discovered that infrared radiation is particularly useful in forming photoablative lesions. In one preferred embodiment the instruments emit radiation at a wavelength in a range from about 800 nm to about 1000 nm, and preferably emit at a wavelength in a range of about 915 nm to about 980 nm. Radiation at a wavelength of 915 nm or 980 nm is commonly preferred, in some applications, because of the optimal absorption of infrared radiation by cardiac tissue at these wavelengths. In the case of ablative radiation that is directed towards the epicardial surface, light at a wavelength about 915 nm can be particularly preferably.
In another aspect of the invention, surgical ablation instruments are disclosed that are well adapted for use in or around the intricate structures of the heart. In one embodiment, the distal end of the instrument can have a malleable shape so as to conform to the surgical space in which the instrument is used. Optional the distal end of the instrument can be shaped into a curve having a radius between about 5 millimeters and about 25 millimeters. The instruments can include at least one malleable strip element disposed within the distal end of the instrument body or housing so that the distal end can be conformed into a desired shape. In addition, the instruments can also include a clasp to form a closed loop after encircling a target site, such as the pulmonary veins.
In yet another aspect of the invention, surgical ablation instruments are disclosed having a housing with at least one lumen therein and having a distal portion that is at least partially transmissive to photoablative radiation. The instruments further include a light delivery element within the lumen of the housing that is adapted to receive radiation from a source and deliver radiant energy through a transmissive region of the housing to a target tissue site. The radiant energy is delivered without the need for contact between the light emitting element and the target tissue because the instruments of the present invention do not rely upon conductive or resistive heating.
The light delivering element can be a light transmitting optical fiber adapted to receive ablative radiation from a radiation source and a light emitting tip at a distal end of the fiber for emitting diffuse or defocused radiation. The light delivering element can be slidably disposed within the inner lumen of the housing and the instrument can further include a translatory mechanism for disposing the tip of the light delivering element at one or more of a plurality of locations with the housing. Optionally, a lubricating fluid can be disposable between the light delivery element and the housing. This fluid can be a physiologically compatible fluid, such as saline, and the fluid can also be used for cooling the light emitting element or for irrigation via one or more exit ports in the housing.
The light emitting tip can include a hollow tube having a proximal end joined to the light transmitting optical fiber, a closed distal end, and an inner space defining a chamber therebetween. The light scattering medium disposed within the chamber can be a polymeric or liquid material having light scattering particles, such as alumina, silica, or titania compounds or mixtures thereof, incorporated therein. The distal end of the tube can include a reflective end and, optionally, the scattering medium and the reflective end can interact to provide a substantially uniform axial distribution of radiation over the length of the housing.
Alternatively, the light emitting tip can include at least one reflector for directing the radiation through the transmissive region of the housing toward a target site and, optionally can further include a plurality of reflectors and/or at least one defocusing lens for distributing the radiation in an elongated pattern.
The light emitting tip can further include at least one longitudinal reflector or similar optical element such that the radiation distributed by the tip is confined to a desired angular distribution.
The hand held instruments can include a handle incorporated into the housing. An inner lumen can extend through the handle to received the light delivering element. The distal end of the instrument can be resiliently deformable or malleable to allow the shape of the ablation element to be adjusted based on the intended use.
In one embodiment, a hand held cardiac ablation instrument is provided having a housing with a curved shape and at least one lumen therein. A light delivering element is disposable within the lumen of the housing for delivering ablative radiation to form a curved lesion at a target tissue site adjacent to the housing.
In another aspect of the invention, the light delivering element can be slidably disposed within the inner lumen of the housing, and can include a light transmitting optical fiber adapted to receive ablative radiation from a radiation source and a light diffusing tip at a distal end of the fiber for emitting radiation. The instrument can optionally include a handle joined to the housing and having an inner lumen though which the light delivering element can pass from the radiation source to the housing.
In another aspect of the present invention, the light diffusing tip can include a tube having a proximal end mated to the light transmitting optical fiber, a closed distal end, and an inner chamber defined therebetween. A light scattering medium is disposed within the inner chamber of the tube. The distal end of the tube can include a reflective end surface, such as a mirror or gold coated surface. The tube can also include a curved, longitudinally-extending, reflector that directs the radiant energy towards the target ablation site. The reflective surfaces and the light scattering medium interact to provide a substantially uniform axial distribution of radiation of the length of the housing.
In other aspects of the present invention, a hand held cardiac ablation instrument is provided having a slidably disposed light transmitting optical fiber, a housing in the shape of an open loop and having a first end adapted to receive the slidably disposed light transmitting optical fiber, and at least one diffuser chamber coupled to the fiber and disposed within the housing. The diffuser chamber can include a light scattering medium disposed within the housing and coupled to the slidably disposed light transmitting optical fiber.
In yet another aspect, a percutaneous cardiac ablation instrument in the form of a balloon catheter with an ablative light projecting assembly is provided. The balloon catheter instrument can include at least one expandable membrane disposed about a housing. This membrane is generally or substantially sealed and serves as a balloon to position the device within a lumen. The balloon structure, when filled with fluid, expands and is engaged in contact with the tissue. The expanded balloon thus defines a staging from which to project ablative radiation in accordance with the invention. The instrument can also include an irrigation mechanism for delivery of fluid at the treatment site. In one embodiment, irrigation is provided by a sheath, partially disposed about the occluding inner balloon, and provides irrigation at a treatment site (e.g. so that blood can be cleared from an ablation site). The entire structure can be deflated by applying a vacuum which removes the fluid from the inner balloon. Once fully deflated, the housing can be easily removed from the body lumen.
The present invention also provides methods for ablating tissue. One method of ablating tissue comprises positioning a distal end of a penetrating energy instrument in proximity to a target region of tissue, the instrument including a source of penetrating energy disposed within the distal end. The distal end of the instrument can be curved to permit the distribution of penetrating energy in elongated and/or arcuate patterns. The method further including activating the energy element to transmit penetrating energy to expose the target region and induce a lesion; and, optionally, repeating the steps of positioning and exposing until a composite lesion of a desired shape is formed.
In another method, a device is provided having a light delivering element coupled to a source of photoablative radiation and configured in a curved shape to emit an arcuate pattern of radiation. The device is positioned in proximity to a target region of cardiac tissue, and applied to induce a curvilinear lesion. The device is then moved to the second position and reapplied to induce a second curvilinear lesion. The steps of positioning and reapplying can be repeated until the lesions are joined together to create a composite lesion (e.g., a closed loop encircling one or more cardiac structures).
In another embodiment, methods of ablating cardiac tissue are provided. A device is provided having a housing in the shape of a hollow ring or partial ring having at least one lumen therein and at least one open end, and a light delivering element slidably disposed within the lumen of the housing for delivering ablative radiation to form a circular lesion at a target region adjacent the housing. The methods includes the steps of positioning the device in proximity to the target region of cardiac tissue, applying the device to the target region to induce a curvilinear lesion, advancing the light delivering element to a second position, reapplying the device to the target region to induce a second curvilinear lesion, and repeating the steps of advancing and applying until the lesions are joined together to create a composite circumferential lesion.